1. Field of the Invention
The present invention relates to a device for controlling number of operating cylinders of an internal combustion engine for a vehicle.
2. Description of the Related Art
There has been proposed a device which controls the number of operating cylinders of an internal combustion engine (hereinafter referred to as an engine) in response to the engine operating condition in order to reduce the fuel consumption of the vehicle engine.
For example, Japanese Patent Apllication Laid-open No. Sho 61-118581 discoloses a device which is equipped with a slider and a pin. The pin engages with or disengages from the slider in a lifter bodies of intake and exhaust valves. When an engine cylinder is put into operation, the pin is driven by an oil pressureunit to engage with the slider by an oil pressure to operate the intake and the exhaust valves. On the other hand when the pin is disengaged from the slider, the valves are put out of
However, if the above structure is installed in an engine, it is necessary to change the engine structure from the ordinary engine structure to a considerable extent. Especially, the engine having multiple intake and exhaust valves for each cylinder requires a substantial alteration.
In addition, when valves of a controlled cylinder stop its operation while other cylinders of the engine are running, the lubricating oil of the suspended cylinder is sucked out since the pressure in the controlled or suspended cylinder becomes negative, thereby causing insufficient lubrication of the cylinder.
In order to provide the above function without considerable change of the driving mechanism, there has been proposed another control device which utilizes exhaust gas to control operation of the cylinders.
Such device is disclosed in Japanese Utility Model Application Laid-open No. 60-52360. The device is equipped with an intake-air-cutoff valve which is driven by a motor to open or close the air-intake passage, an exhaust-gas-intake passage which returns the exhaust gas from the exhaust-side of the suspended cylinder to a downstream portion of the intake-air-cutoff valve and an exhaust-gas-cutoff valve which is driven by a driving unit to open or close the exhaust-gas-intake passage. A driving unit is provided in addition to a motor for driving the intake-air-cutoff valve. When the intake-air-cutoff valve opens and the exhaust-gas-cutoff valve closes, all cylinders of the engine operate. On the other hand, when the intake-air-cutoff valve closes and the exhaust-gas-cutoff valve opens, a set number of cylinders are suspended and the exhaust gases (or air) return through the exhaust-gas-intake passage to the suspended cylinders.
Although the exhaust gas (or air) circulating type device described above does not require a considerable change from the ordinary engine structure, it requires two driving units and additional cost for providing the units.
In addition, the intake-air-cutoff valve must be closed before the exhaust-gas-cutoff valve is opened since the pressure in the controlled or suspended cylinder becomes negative, in order to have the exhaust gas circulation in the suspended cylinder, while the exhaust-gas-cutoff valve must be closed before the intake-air cutoff valve is opened in order to restore the suspended cylinder to operation. Thus, an electronic valve control unit is necessary to control the sequence of the above mentioned valve operation, and, therefore, sensors for sensing the opening or closing of the valves are also necessary.
In other words, an engine can only change over from the full-cylinder operation to the partial-cylinder operation after the intake-air-cutoff valve has been closed by the motor and subsequently the exhaust-gas-cutoff valve is opened by a different driving unit after the intake-air-cutoff is detected by the sensor, and the engine can only return to the full-cylinder operation after the exhaust-gas-cutoff valve has been closed by the different driving unit and the intake-air cutoff valve is subsequently opened by the motor after the exhaust-gas-cutoff state is detected by the sensor.
Since it takes relatively long time for the cutoff valves and the driving units to operate after receiving control signals from the sensor, a comparatively long time period is necessary to change over the engine operation between the full-cylinder-engine operation and the partial-cylinder-engine operation.
As a result, torque shocks, slow response or stagnation of the engine operation may be caused when the changeover of the engine operation between the full-cylinder operation and the partial cylinder operation is initiated.